Production and use of octafluoropropane

a technology of octafluoropropane and octafluoropropane, which is applied in the field of production and use of octafluoropropane, can solve the problems of reducing the yield and selectivity of the objective octafluoropropane, unable to obtain high-purity octafluoropropane, and difficult production of high-purity octafluoroprop

Inactive Publication Date: 2004-04-13
SHOWA DENKO KK
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

In the process for producing octafluoropropane of the present invention (I), a step (1) of reacting hexafluoropropene with hydrogen fluoride in a gas phase at a temperature of from 150 to 450.degree. C. in the presence of a fluorination catalyst to obtain 2H-heptafluoropropane is first performed. Step (1) has the following two advantageous points.
[2] As described above, hexafluoropropene contains compounds having chlorine atom within the molecule as impurities in many cases and these compounds are difficult to remove by a distillation operation. In the present invention, at the same time as the reaction of adding hydrogen fluoride to hexafluoropropene to obtain 2H-heptafluoropropane as an intermediate, compounds having a chlorine atom within the molecule are fluorinated using the hydrogen fluoride and thereby converted into compounds which are easy to separate by distillation.
The fluorination catalyst may be a commonly used chromium-based catalyst. In the case where hexafluoropropene contains chlorine-containing impurities and the chlorine-containing impurities are fluorinated and thereby converted into other compounds, the reaction temperature becomes higher, therefore, a bulk catalyst mainly comprising an oxide of chromium and obtained by adding at least one member selected from indium, zinc and nickel is preferably used, because this catalyst has excellent activity (performance) and high stability (catalyst life). A supported catalyst (e.g. on an alumina support) may also be used, however, a bulk catalyst is preferred in view of activity and stability. Such a catalyst may be activated by a fluorination treatment with hydrogen fluoride before use in the reaction.
As is apparent from Table 2, there is obviously a large difference in boiling point between 2H-heptafluoropropane as an intermediate and the compounds fluorinated according to the above-described reactions, as a result, separation of these compounds by distillation is facilitated.
The step (2) is a direct fluorination reaction step of reacting 2H-heptafluoropropane obtained in the fluorination step of the step (1) with fluorine gas in the gas phase at a temperature of from 250 to 500.degree. C. in the absence of a catalyst to obtain octafluoropropane. This step has the following three advantageous points.
[3] In the direct fluorination reaction of reacting 2H-heptafluoropropane with fluorine gas, if 2H-heptafluoropropane is used in excess based on the fluorine gas, a step of removing fluorine gas may be dispensed with but great difficulties are incurred in the later separation and purification. In the step (2) of the present invention (I), the fluorine gas can be used in an excess molar amount based on 2H-heptafluoropropane so as to elevate the reaction efficiency and when fluorine gas is used in excess, the reaction production gas outflowing from the reaction step contains the excess fluorine gas in addition to perfluorocarbon and hydrogen fluoride. For treating the excess fluorine gas, a method of reacting the gas with an inorganic oxide such as alumina or soda lime is known, however, this method is not preferred because water is produced by the reaction and causes corrosion of apparatus materials. In the present invention (I), the excess fluorine gas can be removed by contacting the gas with hydrofluorocarbon at 1.1 molar times, in terms of the chemical equivalent ratio, to the excess fluorine gas.

Problems solved by technology

However, in these methods, by-products such as tetrafluoromethane (CF.sub.4) and hexafluoroethane (C.sub.2 F.sub.6) are produced due to cleavage, C.sub.6 F.sub.12 and C.sub.6 F.sub.14 are produced due to radical addition, and a 4-membered ring is produced due to cyclization addition, for example, and as a result, the yield of and selectivity for the objective octafluoropropane decrease.
Furthermore, some compounds in these impurities are difficult to separate by distillation and, in turn, high-purity octafluoropropane can hardly be obtained.
Particularly, in the case of using hexafluoropropene as the starting material, chloropentafluoroethane (CFC-115) contained as an impurity scarcely reacts with fluorine gas and mostly remains in the objective octafluoropropane and since this impurity compound can hardly be separated by distillation, due to the similar boiling points, production of high-purity octafluoropropane is difficult.

Method used

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Examples

Experimental program
Comparison scheme
Effect test

example 1

Into an Inconel 600-type reactor having an inner diameter of 1 inch and a length of 1 m, 100 ml of the catalyst, prepared according to the method described in the above Production of Fluorination Catalyst, was filled, and the temperature was elevated to 400.degree. C. while passing nitrogen therethrough. Thereto, hydrogen fluoride was fed at 6.32 NL / hr and then the gas mainly comprising hexafluoropropene as described in Starting Material Example 1 was fed at 3.24 NL / hr. By stopping the feeding of nitrogen gas, the reaction was initiated. After 2 hours, the discharged gas was washed with an aqueous potassium hydroxide solution to remove the acid content and thereafter, the gas composition was analyzed by gas chromatography and, as a result, a gas having the composition shown in Table 5 was obtained.

The gas after the removal of acid content was collected under cooling using a cylinder container and distillation-purified to remove low boiling fractions and high boiling fractions by a k...

example 2

Using the gas mainly comprising 2H-heptafluoropropane after the distillation obtained in Example 1, a direct fluorination reaction with fluorine gas was performed.

A nickel reactor having an inner diameter of 20.6 mm.phi. and a length of 500 mm (using heating by an electric heater; the reactor had been subjected to a passivation treatment with fluorine gas at a temperature of 500.degree. C.) was heated to a temperature of 400.degree. C. while passing nitrogen gas at 20 NL / hr.

Then, hydrogen fluoride (diluting gas) was fed at 60 NL / hr through two branches and, into one gas flow, the gas mainly comprising 2H-heptafluoropropane was fed at 3.24 NL / hr. Thereafter, fluorine gas was fed into another gas flow of hydrogen fluoride at 3.55 NL / hr, the feeding of nitrogen gas was stopped, and the direct fluorination reaction was performed. After 3 hours, the reaction product gas was washed with an aqueous potassium hydroxide solution and an aqueous potassium iodide solution, analyzed on hydrogen ...

example 3

Into a nickel reactor having an inner diameter of 20.6 mm.phi. and a length of 500 mm, the outlet gas containing unreacted fluorine gas obtained after the direct fluorination reaction in Example 2 was introduced. The gas composition was such that the hydrogen fluoride flow was 62.82 NL / hr, the organic material flow was 3.16 NL / hr and the unreacted fluorine gas flow was about 0.26 NL / hr. The reactor temperature was elevated to 390.degree. C., trifluoromethane as hydrofluorocarbon was fed at about 0.286 NL / hr from the reactor inlet, and unreacted fluorine and organic material composition were analyzed by titration and gas chromatography. The amount of unreacted fluorine gas in the outlet gas after the reaction with trifluoromethane was 50 ppm or less, and the outlet gas had the composition shown in Table 9.

Subsequently, the outlet gas after the removal of remaining fluorine gas was washed with an aqueous potassium hydroxide solution to remove hydrogen fluoride. The gas after the remov...

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Abstract

Octafluoropropane is produced by a process comprising a step (1) of reacting hexafluoropropene with hydrogen fluoride in a gas phase at a temperature of from 150 to 450° C. in the presence of a fluorination catalyst to obtain 2H-heptafluoropropane and a step (2) of reacting 2H-heptafluoropropane obtained in step (1) with fluorine gas in a gas phase at a temperature of from 250 to 500° C. in the absence of a catalyst to obtain octafluoropropane. High-purity octafluoropropane is obtained which can be used in a process for producing a semiconductor device.

Description

The present invention relates to a process for producing octafluoropropane, an octafluoropropane product, and uses thereof.Octafluoropropane is used, for example, as a dry-etching or cleaning gas in the process for producing a semiconductor device. With respect to the production methods thereof, the following methods are known:(1) a method of performing a direct fluorination reaction between hexafluoropropene and fluorine gas (see, Japanese Examined Patent Publication No. 62-61572 (JP-B-62-61572)),(2) a method of performing an electrolytic fluorination of hexafluoropropene in hydrogen fluoride (see, Japanese Examined Patent Publication No. 62-61115 (JP-B-62-61115)),(3) a method of reacting hexafluoropropene with fluorine in the presence of a catalyst (see, Japanese Examined Patent Publication No. 1-45455 (JP-B-1-45455)), and(4) a method of reacting hexafluoropropene with a high-order metal fluoride (see, Japanese Examined Patent Publication No. 62-54777 (JP-B-62-54777)).However, in ...

Claims

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Application Information

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Patent Type & Authority Patents(United States)
IPC IPC(8): C07C17/10C07C19/00C07C17/38C07C17/383C07C17/21C07C17/087C07C17/00C07C19/08C07C17/20
CPCC07C17/087C07C17/10C07C17/206C07C17/21C07C17/38C07C17/383C07C19/08
Inventor OHNO, HIROMOTOOHI, TOSHIO
Owner SHOWA DENKO KK
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